The present invention relates to a method of copy protecting an optical disc carrying content and control data and to such a copy protected optical disc.
There are many techniques for copy protecting optical discs. For example, WO 00/74053 proposes copy protecting audio data on a digital audio compact disc (CD-DA) by rendering control data encoded onto the disc incorrect and/or inaccurate. The incorrect data encoded onto the CD is either inaccessible to, or not generally used by, a CD-DA player. Therefore a legitimate audio CD can be played normally on a compact disc music player, but the incorrect data renders the protected audio data on the CD unplayable by a CD-ROM drive.
As this earlier copy protection method prevents the user from using a CD-ROM drive legitimately simply to play the music or other audio on a CD-DA, alternative methods of copy protection have been proposed which, whilst preventing the production of usable copy discs, do not prevent or degrade the playing of legitimate optical discs on all players having the functionality to play such optical discs. Examples of such copy protection methods are described in WO 01/61695 and in WO 01/61696.
These further methods remove, corrupt, or otherwise render inaccurate control data associated with the information on the disc.
It is also known to provide a copy protected disc where at least one region of the content contains unreadable or subversive data, and access to these regions of unreadable or subversive data is prevented during normal playback of the disc. Similarly, however, copying techniques are now known where it is possible to parse the navigation structure on a disc and select the main feature by choosing, for example, a program chain having the longest presentation time, hence skipping any unnecessary or subversive data. This makes the copying process quite straightforward, as no knowledge of the navigation structure of a DVD is required and all unwanted content such as copyright warnings or trailers may be skipped while copying. This copying technique is known as IFO parsing ripping.